Le traitement des gliomes de haut grade représente un réel défi médical. Les techniques de thérapies actuelles sont principalement à visée palliative et leur efficacité est limitée. De nombreuses stratégies thérapeutiques sont explorées pour trouver un traitement curatif. La radiothérapie stéréotaxique par rayonnement synchrotron (SSRT) est une technique innovante dont le principe repose sur l'accumulation sélective d'un élément lourd (Z élevé) dans la tumeur, suivie d'une irradiation stéréotaxique avec un faisceau monochromatique de rayons X, de faible énergie (50-100 keV), issus d'une source synchrotron. Une augmentation de la dose déposée localement dans la tumeur est obtenue grâce au renforcement de l’effet photoélectrique dans ces conditions. Cette thèse s’inscrit dans le cadre des essais cliniques de phase I et II de la SSRT menés sur des métastases cérébrales, au synchrotron européen à Grenoble. Une injection systémique d’un agent de contraste iodé et un faisceau synchrotron de 80 keV sont utilisés lors de ces essais. L’efficacité de la SSRT repose directement sur la concentration de l’agent de contraste iodé accumulé dans la tumeur, sa stabilité au cours du temps et sa reproductibilité chez le même patient. L’objectif principal de ce travail a été d’évaluer et de modéliser les concentrations d'iode moyennes atteintes dans des métastases cérébrales, d’une part, et d’appréhender les impacts dosimétriques, engendrés par les variations spatiales et temporelles de ces concentrations sur le traitement des patients, d’autre part. Un protocole d'imagerie scanner a été conçu spécifiquement pour cette étude afin de permettre le suivi, temporel et spatial, des concentrations d'iode et l’extraction des paramètres de perfusion cérébrale dans une métastase cérébrale. Une méthodologie d'analyse expérimentale et une modélisation théorique de la bio-distribution d'iode dans des métastases cérébrales ont été développées. Un modèle mathématique reliant les concentrations d'iode aux paramètres de perfusion a été établi, dans le but de prédire les concentrations d'iode chez chaque patient et de réduire la durée du protocole de suivi. La reproductibilité de la prise de contraste a été caractérisée chez des patients à dix jours d’intervalle. Les impacts dosimétriques des écarts de concentrations d'iode observés sur les plans de traitement en SSRT ont été analysés. Ces derniers ont été comparés aux plans de traitement obtenus avec différentes techniques de pointe en radiothérapie afin d’évaluer les performances dosimétriques de la SSRT. / Gliomas treatment is still a challenging disease in medicine. Available treatments are mainly palliative and their efficiency is limited. Since years, many therapeutic strategies have been explored to find a cure. Synchrotron stereotactic radiotherapy (SSRT) is an innovative treatment combining the selective accumulation of heavy elements in tumours with stereotactic irradiations using monochromatic medium energy x-rays from a synchrotron source. A localised dose enhancement in brain tumours is obtained due to the reinforced photoelectric absorption in these conditions. This thesis takes part in the framework of phase I/II clinical trials, which are underway at the European Synchrotron Radiation Facility in Grenoble, France. These trials are realised on human brain metastasis using venous infusion of iodinated contrast agents and a 80 keV X-ray beam. The radiation dose enhancement depends on the amount of iodine in the tumour, its time course and its reproducibility for each patient. The aim of this work was to evaluate and model the amounts of iodine concentrations reached in brain metastasis, and to analyse the dosimetric deviations caused by spatial and temporal variations of these concentrations during the treatments. A CT cine scan protocol was designed especially for this study in order to extract quantitative iodine concentrations and associated brain perfusion parameters in human brain metastasis, as key parameters for treatment feasibility and quality. An experimental analysis methodology and a theoretical model of iodine biodistribution were developed. A mathematical relationship between iodine concentrations and perfusion parameters was established in order to estimate these concentrations for each patient in the future and to reduce the imaging dose, associated to the prolonged imaging acquisition time. The reproducibility of iodine uptake between the CT planning scan day and the treatment day was assessed (~10 days interval). The impact of iodine concentration variations on reference SSRT dosimetries was analysed. Finally, SSRT treatment plans were compared to those obtained with different cutting-edge radiotherapy techniques in order to evaluate dosimetric performances of SSRT.

L'ingénierie tissulaire représente une solution prometteuse pour la production de substituts osseux. L'utilisation de bioréacteurs à perfusion pour cultiver des cellules ostéo-compétentes sur des matrices poreuses, permet de résoudre les limitations dues au transfert de masse, et d'apporter des stimuli physiques améliorant la prolifération et la différenciation cellulaire. Malgré les récents et importants développements des bioréacteurs en ingénierie tissulaire, les mécanismes menant à la production de substituts osseux en bioréacteurs restent mal compris.Le but de cette thèse est d'améliorer la compréhension de l'influence des phénomènes de transport, sur la croissance cellulaire et tissulaire dans un bioréacteur à perfusion. Dans cet objectif, une approche combinant modélisation et expérimentation est proposée.Dans un premier temps, un cadre théorique rigoureux est développé afin d'étudier les propriétés de transport du bioréacteur. Etant donné la nature hiérarchique du système, l'aspect multi-échelle du problème doit être pris en compte. En se basant sur la méthode de prise de moyenne volumique avec fermeture, les processus de transport d'espèce et de quantité de mouvement sont homogénéisés à partir de l'échelle de la matrice extracellulaire, jusqu'à l'échelle du bioréacteur. Les propriétés effectives des différentes structures rencontrées sont évaluées, et l'influence des dépendances inter-échelles sont mises en valeur. Le model macroscopique obtenu inclus des termes non-conventionnels, dont les contributions sont évaluées pour les conditions de fonctionnement du bioréacteur.Dans un second temps, la prolifération cellulaire et la production de tissu sont étudiées d'un point de vue expérimentale et théorique. Premièrement, des cellules de type fibroblaste, sont cultivées jusqu'à trois semaines sur des billes de verre, dans un bioréacteur perfusé à 10mL/min. Un protocole combinant des techniques d'histologie et d'analyse d'image, permet de quantifier la croissance de cellules et de tissu en fonction du temps et de l'espace. Deuxièmement, une cinétique de production de tissu est introduite dans le modèle de transport multiéchelle développé plus tôt. Finalement, la résolution à l'échelle du bioréacteur permet de discuter les résultats expérimentaux et théoriques au regard des phénomènes de transport ayant lieux dans le bioréacteur à perfusion. / Tissue engineering represents a promising approach for the production of bone substitutes. The use of perfusion bioreactors for the culture of bone-forming cells on a three-dimensional porous scaffold material, resolves mass transport limitations and provides physical stimuli, increasing the overall proliferation and differentiation of cells. Despite the recent and important development of bioreactors for tissue engineering, the underlying mechanisms leading to the production of bone substitutes remain poorly understood. The aim of this thesis is to gain insight on the influence of transport phenomena, on cell and tissue growth within a perfusion bioreactor. To this purpose, a combined modeling and experimental approach is followed.To start with, a rigorous theoretical framework is developed in order to study the transport properties of the bioreactor. Given the hierarchical nature of the system, the multiscale aspect of the problem must be taken into account. Based on the volume averaging theory with closure, mass and momentum transport processes are upscaled from the extracellular matrix scale, to the bioreactor scale. The effective properties of the encountered structures are evaluated, and the influence of the interscale dependencies are emphasized. The resulting macroscopic model includes non-conventional terms, which contributions are evaluated in the case of the bioreactor culture conditions.Then, cell proliferation and tissue growth are studied both, from an experimental and modeling point of view. First, fibroblast cells are cultured on glass beads in a bioreactor, perfused with culture medium at 10mL/min, for up to three weeks. A protocol combining histological techniques and image analysis allows the quantification of cell and tissue growth as a function of space and time. Second, a theoretical tissue production kinetic is introduced in the multiscale transport model previously developed. Finally, the resolution at the bioreactor scale allows to discuss the theoretical and experimental results in regard to the transport phenomena taking place in the perfusion bioreactor.

Le but de cette étude est de proposer un modèle combiné au transfert de chaleur dans la veine et des tissus de la peau humaine. Il permet de mieux comprendre le comportement thermomécanique de la peau et de son environnement direct lorsqu'ils sont exposés à de fortes variations thermiques. Le travail est basé sur des études expérimentales et numériques. La première étape expérimentale consiste à placer une barre d'acier cylindrique refroidie ou réchauffée sur la peau d'un avant-bras humain et en mesurant l'évolution de température en utilisant une caméra infrarouge. L'influence de la circulation sanguine dans les veines sur la diffusion de la chaleur est très nettement.La deuxième étape expérimentale consiste à mesurer les propriétés géométriques des veines et la vitesse du sang en utilisant une sonde d'écho-Doppler. Ces mesures expérimentales fournissent un modèle numérique de la peau et de son environnement direct. Le modèle tridimensionnel multicouche utilise l'équation biothermique de Pennes pour modéliser les tissus et celle de la chaleur dans un fluide pour modéliser le sang. Les propriétés des matériaux sont tirées de la littérature et validées par notre expérimentation. Le modèle numérique permet de retrouver les mesures expérimentales, mais aussi d'accéder à la température et à la vitesse du sang dans les veines. Enfin, un modèle numérique d'endommagement thermique, couplé au modèle multicouche de la peau, a été développé dans cette étude. Il permet de simuler l'endommagement suite à une brûlure de la peau et de tester l'efficacité de différents traitements visant à limiter les lésions. / The aim of this study is to propose a combined model of heat transfer in the vein and tissue of human skin. It allows to better understand the thermomechanical behavior of the skin and its direct environment when exposed to strong thermal variations. The work is based on experimental and numerical investigations. The first experimental step consists in placing a cooled or a heated cylindrical steel bar on the skin of a human forearm and measuring the temperature change using an infrared camera. Blood circulation in the veins was seen to clearly influence heat diffusion. The second experimental step consists in measuring geometrical properties of the veins and blood velocity using an echo-Doppler probe. These experimental measurements provide a numerical model of the skin and its direct vicinity. The three-dimensional multilayer model uses Pennes equation to model biological tissue and the convective heat transport equation, to model blood. The properties of the biological materials obtained from the literature are validated by our experimentation. The numerical model is able to simulate the experimental observations, but also to estimate blood temperature and velocity in the veins. Finally, a numerical model of thermal damage, coupled with the multilayer model of skin, was developed in this study. It simulates the damage due to burning of the skin and to test the efficacy of different treatments to limit the damage.

L'IRM de perfusion et de spectroscopie restent encore peu utilisées en raison de leur mise en oeuvre difficile et de leur manque de quantification. L'objectif de ces travaux a été d'optimiser et de valider des techniques IRM totalement non invasives chez l'Homme en vue d'applications cliniques permettant une exploration sur un large volume cérébral et une quantification absolue des paramètres de perfusion et du métabolisme cérébraux. Concernant la perfusion, 3 séquences de type marquage de spins,PASL PICORE, PASL FAIR et pCASL, ont été comparées en termes de sensibilité et de reproductibilité. pCASL a ensuite été intégrée dans un protocole de recherche sur des patients atteints de sclérose en plaques ou SEP. Quant au métabolisme cérébral, un protocole a été mis en place afin d'accéder à une quantification absolue et pseudo absolue des métabolites par la normalisation du signal de l'eau issue de la CSI par la densité de protons acquise en IRM. Cette technique a été validée en CSI 2D puis transposée en 3D avec la séquence EPSI sur deux orientations différentes : CACP et CACP+15°afin de constituer des valeurs normatives fiables des métabolites principaux sur tout le cerveau. L'élaboration de ces techniques en spectroscopie a abouti à une étude sur des patients souffrant de SEP démontrant la faisabilité de l'utilisation de ces techniques en clinique. Ces travaux démontrent que la quantification absolue en IRM de perfusion et en IRM de spectroscopie peut être obtenue sur un large volume cérébral de manière fiable sur un système IRM disponible en environnement clinique dans un temps d'acquisition acceptable à travers les corrections diverses spécifiques à chaque imagerie. / Conventional MRI's lack of specificity in clinical routine limits our ability to perform correct diagnoses or follow-ups of pathological diseases. Two forms of NMR imaging, perfusion weighed and spectroscopic imaging provide information about two closely related characteristics :cerebral perfusion and metabolism. However, these techniques are not widely used due to the complexity of implementation and a lack of quantification.The general aim was to optimize and validate completely non-invasive NMR techniques for further human clinical applications in the context of exploring large cerebral volumes and determining absolute or pseudo-absolute quantification of cerebral perfusion and metabolism. Concerning perfusion, three arterial spin labeling sequences, PASL PICORE, PASL FAIR and pCASL, were compared in terms of sensitivity and reproducibility. The pCASL sequence was then integrated to a protocol applied to patients suffering from multiple sclerosis. In relation to metabolism, a protocol was applied in order to access absolute and pseudo-absolute metabolite quantification by water SI normalization from MRI proton density. This technique was validated on 2D CSI and then on 3D with EPSI sequence with two orientations, AC-PC and AC-PC+15 in order to generate reliable normative values of metabolites for the whole brain. The use of those spectroscopic techniques on patients suffering from multiple sclerosis allowed demonstrating the feasibility in clinic.This work demonstrates that reliable absolute quantification in perfusion weighted and spectroscopic imaging can be obtained with extensive coverage and with an acquisition time compatible with the reality of clinical exams.

Orientador: Renato Guiseppe Terzi / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas / Made available in DSpace on 2018-08-07T22:34:54Z (GMT). No. of bitstreams: 1 Ferreira_JulianaHeloisaTerra_M.pdf: 2639255 bytes, checksum: fcee62586088020b3a17254a5a9df91f (MD5) Previous issue date: 2006 / Resumo: A literatura aborda de forma muito ampla os mecanismos responsáveis pela gênese da hipoxemia no tromboembolismo pulmonar (TEP). O objetivo deste estudo foi analisar quais os mecanismos que contribuíram para a hipoxemia em um modelo de TEP agudo experimental. A embolização com coágulos autólogos foi realizada em sete porcos com peso de 24,00±0,6 kg, anestesiados e mecanicamente ventilados na modalidade controlada, com fração de oxigênio no ar inspirado (FiO2) de 0,21. A análise do intercâmbio gasoso foi realizada pela correlação entre a gasometria arterial e a capnografia volumétrica. Foi observada uma significativa redução das pressões parciais de oxigênio tanto no sangue arterial quanto no ar alveolar calculada pela equação do ar alveolar. A ventilação alveolar efetiva apresentou significativa redução, evidenciando a consistente queda do volume de gás alveolar que efetivamente participou das trocas gasosas (VAef). A relação entre a ventilação alveolar que efetivamente participou das trocas gasosas e o débito cardíaco (V¿Aef/Q¿), também apresentou uma redução significativa após a embolização. Embora a pressão parcial de dióxido de carbono (CO2) no sangue arterial aumente significativamente, a pressão parcial de CO2 no final da expiração (PetCO2) apresentou significativa redução, retornando ao basal aos quarenta minutos após a embolia. Conseqüentemente, a diferença artério-alveolar de pressão parcial de dióxido de carbono (P(a-et)CO2) aumentou significativamente. Houve um aumento de espaço morto alveolar e fisiológico. Concluímos, com base nos dados obtidos que a grave hipoxemia arterial observada pode ser explicada por redução da pressão alveolar de oxigênio, além da redução da ventilação alveolar efetiva e da razão V¿Aef/Q¿. Também demonstramos que a razão V¿Aef/Q¿ aumentou progressivamente depois da embolização, um fato atribuído, ou por lise dos trombos, ou por redistribuição da ventilação alveolar induzida por broncoconstrição hipocápnica / Abstract: The literature broadly approaches the mechanisms responsible for the genesis of the hypoxemia in pulmonary embolism (PE). The aim of this study is to analyze the ventilation/perfusion ratio, which contributed to the hypoxemia in PE by analyzing blood gases and volumetric capnography in a model of experimental acute PE. Pulmonary embolization with autologous blood clots was carried out in seven pigs weighing 24.00±0.6Kg, anesthetized and mechanically ventilated. A significant reduction in the oxygen partial pressures was observed in both, the arterial blood and alveolar air. The effective alveolar ventilation exhibited a significant reduction consistent with the fall in the alveolar gas volume that effectively participated in gas exchange. The relation between the alveolar ventilation that effectively participated in gas exchange and cardiac output (V¿Aeff/Q¿ ratio) also presented a significant reduction after embolization. The carbon dioxide partial pressure increased significantly in the arterial blood (PaCO2), but decreased significantly in the exhaled air at the end of the respiratory cycle (PetCO2). PetCO2 returned to baseline values forty minutes after embolism. The arterial to alveolar carbon dioxide gradient (P(a-et)CO2), increased significantly, as well as the calculated alveolar and physiological dead spaces. We conclude, based on our data, that the severe arterial hypoxemia observed in this experimental model may be attributed to the reduction of the effective alveolar ventilation ratio (V¿Aeff/Q¿). We were also able to demonstrate that V¿Aeff/Q¿ progressively improves after embolization, a fact attributed to the lysis of thromby or by alveolar ventilation redistribution induced by hypocapnic bronchoconstriction / Mestrado / Pesquisa Experimental / Mestre em Cirurgia

L’expansion volémique est le traitement de première intention de l’insuffisance circulatoire aiguë dans presque tous les cas. Cependant, son efficacité très inconstante et ses effets secondaires incitent à en prédire les effets avant de l’entreprendre. Plusieurs tests ont été développés pour détecter cet état de précharge dépendance, et nous nous sommes intéressés au perfectionnement de certains d’entre eux et à la description de leurs limites.Le test de passive leg raising (PLR) repose sur le transfert de sang veineux depuis le territoire veineux splanchnique et les membres inférieurs vers le thorax. Nous avons démontré qu’en cas d’hypertension intra-abdominale, la valeur diagnostique du test était plus faible, avec l’apparition de nombreux cas de faux négatifs. Cette limite du PLR test est importante en raison de la prévalence de l’hypertension intra-abdominale chez les patients de soins intensifs.Les effets de ce test doivent être appréciés sur le débit cardiaque, et plusieurs méthodes ont déjà été décrites pour cela. Nous avons d’abord pu montrer que celle qui consiste à mesurer les effets du test sur les débits artériels carotidien et fémoral n’était pas fiable, avec une très mauvaise corrélation entre les changements de débit cardiaque et ceux de ces deux débits artériels. En revanche, nous avons décrit une méthode originale et fiable pour mesurer les effets du test, qui consiste en la mesure de l’indice de perfusion (IP), rapport entre la portion pulsatile et non pulsatile du signal de saturation pulsée en oxygène. Même si le signal ne pouvait pas être recueilli de façon stable chez tous les patients, les changements de cet indice lors du PLR permettaient de mesurer ses effets et de détecter la précharge dépendance. Ces résultats ouvrent la possibilité de mesurer les effets du test grâce à un outil non-invasif et pouvant être utilisé chez tous les patients en réanimation et au bloc opératoire.Enfin, nous avons appliqué la mesure de l’IP à un autre test détectant la précharge dépendance, le test d’occlusion télé-expiratoire. Il consiste à interrompre la ventilation mécanique pendant quelques secondes et à observer les changements simultanés du débit cardiaque. Même s’ils sont de plus faible amplitude que ceux induits par le PLR, ces changements étaient correctement suivis par les modifications de l’IP et ils détectaient de façon fiable la précharge dépendance. / Volume expansion is the first-line treatment of acute circulatory failure in almost all cases. However, its inconsistent effectiveness and side effects encourage to predict its effects before undertaking it. Several tests have been developed to detect preload responsiveness and we have sought to improve some of them and describe their limits.The passive leg raising (PLR) test is based on the transfer of some venous blood from the venous compartment of the splanchnic compartment and the lower limbs toward the thorax. We have shown that, in case of intra-abdominal hypertension, the diagnostic value of the test was lower, with many cases false negatives cases. This limitation of the PLR test is of importance because of the prevalence of intra-abdominal hypertension in critically ill patients.The effects of this test should be evaluated on cardiac output, and several methods have already been described for this evaluation. First, we have shown that measuring the effects of the test on carotid and femoral arterial flows was unreliable, with a very poor correlation between changes in cardiac output and those in these two arterial flows. Second, we have described an original and reliable method for measuring the effects of the test, which consists in measuring the perfusion index (PI), the ratio between the pulsatile and non-pulsatile portions of the pulse oximetry signal. Although a stable signal could not be obtained in all patients, changes in this index during PLR allowed the measurement of its effects and the detection of preload responsiveness. These results open up the possibility of measuring the effects of the test with a non-invasive tool that can be used in all patients in the intensive care unit and the operating room.Finally, we applied the PI measurement to another test of preload responsiveness, the end-expiratory occlusion test. It consists in interrupting mechanical ventilation for a few seconds and observing simultaneous changes in cardiac output. Although the changes are smaller than those induced by PLR, these changes were well tracked by PI changes and reliably detected preload dependence.

Les techniques d'imagerie par résonance magnétique de Diffusion (IRMd) et de Perfusion (IRMp) permettent la détection de divers aspects importants et complémentaires en imagerie cérébrale. Le travail effectué dans cette thèse présente des contributions théoriques et méthodologiques sur les modalités d'IRM basées sur des images pondérées en diffusion, et sur des images de perfusion par injection de produit de contraste. Pour chacune des deux modalités, les contributions de la thèse sont liées au développement de nouvelles méthodes pour améliorer la qualité, le traitement et l'exploitation des signaux acquis. En IRM de diffusion, la nature complexe du signal est étudiée avec un accent sur l'information de phase. Le signal complexe est ensuite exploité pour corriger le biais induit par le bruit d'acquisition des images, améliorant ainsi l'estimation de certaines métriques structurelles. En IRM de perfusion, le traitement du signal est revisité afin de tenir compte du biais dû à la dispersion du bolus. On montre comment ce phénomène, qui peut empêcher la correcte estimation des métriques de perfusion, peut aussi donner des informations importantes sur l'état pathologique du tissu cérébral. Les contributions apportées dans cette thèse sont présentées dans un cadre théorique et méthodologique validé sur de nombreuses données synthétiques et réelles. / Diffusion and Perfusion Magnetic Resonance Imaging (dMRI & pMRI) represent two modalities that allow sensing important and different but complementary aspects of brain imaging. This thesis presents a theoretical and methodological investigation on the MRI modalities based on diffusion-weighted (DW) and dynamic susceptibility contrast (DSC) images. For both modalities, the contributions of the thesis are related to the development of new methods to improve and better exploit the quality of the obtained signals. With respect to contributions in diffusion MRI, the nature of the complex DW signal is investigated to explore a new potential contrast related to tissue microstructure. In addition, the complex signal is exploited to correct a bias induced by acquisition noise of DW images, thus improving the estimation of structural scalar metrics. With respect to contributions in perfusion MRI, the DSC signal processing is revisited in order to account for the bias due to bolus dispersion. This phenomenon prevents the correct estimation of perfusion metrics but, at the same time, can give important insights about the pathological condition of the brain tissue. The contributions of the thesis are presented within a theoretical and methodological framework, validated on both synthetical and real images.

Imaging photoplethysmography (iPPG) has attracted much attention over the last years. The vast majority of works focuses on methods to reliably extract the heart rate from videos. Only a few works addressed iPPGs ability to exploit spatio-temporal perfusion pattern to derive further diagnostic statements. This work directs at the spatio-temporal analysis of blood perfusion from videos. We present a novel algorithm that bases on the two-dimensional representation of the blood pulsation (perfusion map). The basic idea behind the proposed algorithm consists of a pairwise estimation of time delays between photoplethysmographic signals of spatially separated regions. The probabilistic approach yields a parameter denoted as perfusion speed. We compare the perfusion speed versus two parameters, which assess the strength of blood pulsation (perfusion strength and signal to noise ratio). Preliminary results using video data with different physiological stimuli (cold pressure test, cold face test) show that all measures are in fluenced by those stimuli (some of them with statistical certainty). The perfusion speed turned out to be more sensitive than the other measures in some cases. However, our results also show that the intraindividual stability and interindividual comparability of all used measures remain critical points. This work proves the general feasibility of employing the perfusion speed as novel iPPG quantity. Future studies will address open points like the handling of ballistocardiographic effects and will try to deepen the understanding of the predominant physiological mechanisms and their relation to the algorithmic performance.

Background: Permanent paraplegia is a rare but feared complication of both open and endovascular thoracoabdominal aortic repair. The rate of postoperative paraplegia varies depending on the extent of open repair, from 0.9% to 4.7%, even in expert centers (Coselli et al. 2016; Etz et al. 2015). Among the currently available protective adjuncts, distal perfusion (DP) and cerebrospinal fluid (CSF) drainage are one of the most widely used ones (Etz et al. 2015). The scientific evidence of DP is based on observational clinical studies with heterogenous patients and perioperative strategies, and few experimental works with various combinations of preventive techniques analyzed simultaneously (Rose et al. 1997; Winnerkvist et al. 2002). Aim of the study: The aim of the study was to evaluate the isolated effect of DP on regional spinal cord perfusion during aortic cross-clamping, and additional deliberate CSF pressure elevation in a large animal model. Additionally, we aimed to assess DP impact on paraspinous muscle perfusion, and evaluate the efficacy of collateral network near-infrared spectroscopy (cnNIRS) as a monitoring technique during DP. Methods: The study was performed in an acute large animal model (8 juvenile female German landrace pigs) via upper left lateral thoracotomy in the 3rd intercostal space, and retroperitoneal access. Distal perfusion was performed using partial cardiopulmonary bypass (CPB) with target perfusion pressure of 60 mmHg. Arterial lines of CPB were placed into the descending thoracic and abdominal aorta, and the venous line – into the pulmonary artery. Lumbar puncture at the L3-L4 level was performed in order to perform plasma injection during CSF pressure elevation stage. Spinal cord and paraspinous muscle regional perfusion was evaluated using microspheres injections (a total of 6 colors) at four experimental time-points: on running CPB (baseline), 5 minutes after proximal aortic cross-clamping, 5 minutes after abdominal aortic cross-clamping and initiation of DP, and after 15 minutes of manually increased (tripled) CSF pressure. During the DP, proximal and distal blood flows were evaluated separately with two microsphere colors injected simultaneously via CPB arterial lines. For the analysis, the spinal cord was divided into three segments: upper (C1-T7), mid- (T8-L2) and lower (L3-S). Paraspinous muscle perfusion and oxygenation were assessed at 4 levels: mid- and lower thoracic, upper and lower lumbar levels. At the end of each experiment, the whole spinal cord and 2 cm3 samples of paraspinous muscles corresponding to the cnNIRS levels, were harvested. Results: Spinal Cord Perfusion: In the upper spinal cord, statistically significant changes of regional perfusion were observed both after DTA cross-clamping (decrease to 62% from baseline), and after distal aortic cross-clamping with initiation of DP (increase to 156% in proximal and decrease to 5% from baseline in distal flow). These were followed by a significant drop of proximal spinal cord perfusion (from 152% back to 102%, p = 0.038), and some increase of distal perfusion values (from 5% to 19%, however not reaching statistical significance) during the CSF pressure elevation stage. In the mid-spinal cord, a notable decrease of perfusion was observed after proximal aortic cross-clamping (to 27%, p = 0.025). The initiation of DP was not associated with any notable changes in proximal and distal perfusion values. Afterwards, a decrease of proximal and distal perfusion values (from 33% to 13% in proximal, and from 24% to 10% in distal perfusion) was observed during CSF pressure elevation stage. These changes were, however, not statistically significant. Lower spinal cord measurements showed, similarly to mid-segment, a decrease in perfusion after DTA cross-clamping (to 14% from baseline, p = 0.001). Initiation of DP led to normalization of proximal perfusion of the lower spinal cord (to 96% from baseline). At the same time, it was associated with extreme hyperperfusion due to distal perfusion (up to 480% from baseline). The tripling of CSF pressure resulted in decrease of both proximal (from 96% to 59%, p = 0.131) and distal (from 480% to 468%, p = 0.999) perfusion rates. Paraspinous muscle perfusion: The analysis of paraspinous muscle (i.e. collateral network) perfusion values revealed few statistically significant changes. Proximal aortic cross-clamping resulted in a decrease of paraspinous muscle perfusion (not reaching statistical significance). The least perfused were lower thoracic and upper lumbar segments. Neither initiation of DP, nor CSF pressure elevation were associated with any statistically significant changes in paraspinous muscles perfusion at any of the analyzed levels, except the lower lumbar one. Here, the distal perfusion increased from 7% to 27% from baseline during DP, and from 27% to 60% during the CSF elevation stage (p = 0.034). cnNIRS: Continuous cnNIRS monitoring did not reveal any notable changes at the mid-thoracic level. At the other three levels, the values decreased after DTA cross-clamping (p < 0.001 according to ANOVA). At the lower thoracic level, the tissue oxygenation values crossed the 70% from baseline ischemic threshold after initiation of DP. CSF pressure elevation did not have any influence on cnNIRS values at any level. Discussion: Comparison of the present experiment with the previously published studies is limited due to discrepancy in experimental sequences, analyzed segments and possible effects of other protective adjuncts used in the studies. However, in the initial phase of the experiment, the decrease of blood flow in all the spinal cord segments, was similar to the previously published works (Brattli et al. 2007; von Aspern et al. 2020). These changes were used as a second, “ischemic” baseline during the present study. Initiation of the DP led to limited or no perfusion increase of spinal cord perfusion in upper (C1-T7) and mid-spinal cord (T8-L2). And, if in the upper spinal cord this could be compensated by increased proximal flow, the mid-spinal cord was the least protected segment. At the same time, it was associated with extreme hyperperfusion (due to distal flow) of the spinal cord in the lumbar segment (L3-S), which is a known risk factor of spinal cord injury itself (Bower et al. 1989; Gallagher et al. 2019). The CSF pressure elevation resulted in further spinal cord tissue perfusion decrease, as previously reported by Haunschild et al. in experiments without aortic cross-clamping and DP (Haunschild et al. 2020). Although these changes were statistically significant only at the upper spinal cord level, they resulted in a pronounced reduction of proximal perfusion also in the other two spinal cord segments. Similarly, the decrease was observed also in distal perfusion in the mid- and lower spinal cord. Summarizing these findings, one would suggest that not only did DP (with 60 mmHg pressure) not lead to adequate protection of the mid-spinal cord during aortic cross-clamping, but it also was not able to protect it in the presence of increased CSF pressure. One also needs to point out, that although elevated CSF pressure led to some decrease of distal flow in lumbar segment, it did not eliminate the hyperperfusion of the spinal cord. In paraspinous muscle perfusion, as previously reported by von Aspern and colleagues, the perfusion reduction was more prominent in the lower thoracic and upper lumbar segments, which corresponds with the spinal cord regional perfusion results. During the next stages, almost no changes were observed in paraspinous muscles perfusion. The exclusion was the lower lumbar level, where some increase of distal perfusion was observed, however not reflecting the hyperperfusion of the spinal cord at this level. As a reflection of collateral perfusion, collateral network oxygenation monitoring using cnNIRS demonstrated limited changes. The most pronounced decrease of oxygenation was observed after aortic cross-clamping, thus following the pattern reported by von Aspern (von Aspern et al. 2020). However, at lower thoracic level, the values did cross the 70% ischemic threshold after initiation of DP, signaling ischemia. Similarly to paraspinous muscle perfusion, cnNIRS was not able to reflect the hyperperfusion of the distal spinal cord. Conclusions: The present study points out, that DP during open thoracoabdominal aortic repair should be managed with caution. It was shown that DP with stable unadjusted perfusion pressure of 60 mmHg does not provide adequate protection at the mid-thoracic level of the spinal cord and could not counteract CSF pressure elevation. At the same time, it may be associated with hyperperfusion of its distal segment. Distal perfusion, both with normal and elevated CSF pressure, did not lead to any significant changes in paraspinous muscles perfusion, except the lower lumbar segment. However, the lowest perfusion values were observed around the mid-spinal cord (the most vulnerable) area. Moreover, despite the fact that cnNIRS was able to reflect severe spinal cord ischemia, it did not reveal the spinal cord hyperperfusion. Further studies, including chronic animal experiments, are required for precise evaluation of DP in various pressure modes, and its ability to counteract the elevated CSF pressure.:Table of contents III List of abbreviations V 1 Introduction 1 1.1 Anatomy of the aorta 1 1.2 Descending thoracic and thoracoabdominal aortic pathology 2 1.3 Open surgical and endovascular treatment of thoracic and thoracoabdominal aortic pathology 4 1.4 Postoperative spinal cord injury 7 1.5 Spinal cord anatomy 9 1.6 Spinal cord blood supply: collateral network concept 10 1.7 Perioperative and adjunctive strategies to prevent spinal cord injury 12 1.8 Swine as an experimental model for spinal cord injury research 15 2 Aim of the study 16 3 Materials 17 3.1 Experimental materials 17 3.1.1 Devices 17 3.1.2 Expendable materials and instruments 18 3.1.3 Medications and chemicals 20 3.2 Laboratory materials 22 3.2.1 Devices 22 3.2.2 Expendable materials and instruments 23 3.2.3 Chemicals 25 3.3 Software 26 4 Methods 27 4.1 Experimental model 27 4.1.1 Experimental animals 27 4.1.2 Anaesthesia 28 4.1.3 Surgical approach and experimental sequence 29 4.1.4 Tissue harvesting and preparation 33 4.2 Analysis during the experiment 33 4.2.1 Microsphere measurements 33 4.2.2 Collateral network near-infrared spectroscopy 38 4.2.3 Histopathological assessment 39 4.2.4 Statistical analysis 42 5 Results 43 5.1 Vital parameters during the experiment 43 5.2 Spinal cord regional perfusion 45 5.3 Collateral network regional perfusion 50 5.4 Collateral network oxygenation 54 5.5 Relationships between regional perfusion and oxygenation values 56 5.6 Histopathological assessment 60 6 Discussion 62 6.1 Discussion of vital parameters during the experiment 64 6.2 Discussion of spinal cord regional perfusion 66 6.3 Discussion of collateral network regional perfusion 71 6.4 Discussion of collateral network oxygenation 73 6.5 Discussion of the relationships between regional perfusion and 75 oxygenation values 6.6 Discussion of histopathological results 76 6.7 Conclusions 77 6.8 Limitations of the study 78 7 Summary 81 8 References 86 9 Figure legends 103 10 Table legends 105 Acknowledgements 106 Declaration about the independent work for dissertation 107 Curriculum vitae 108

La transplantation est la meilleure alternative en cas d'insuffisance rénale terminale. Face à la pénurie de greffons, les équipes de transplantation se sont tournées notamment vers les donneurs décédés par arrêt circulatoire (DDAC) non contrôlés. Ces greffons soumis à une période d'ischémie chaude sont plus fragiles. Des méthodes de reconditionnement chez le donneur par refroidissement in situ (RIS) et circulation régionale normothermique (CRN) se sont développées afin de réduire les lésions d'ischémie-reperfusion. Le choix de la méthode est laissé à l'appréciation de chaque équipe et il existe une grande hétérogénéité des pratiques. Après prélèvement, l'utilisation des machines de perfusion hypothermique (MPH) est généralement recommandée. L'optimisation de ces phases de reconditionnement chez le donneur et de conservation hypothermique apparait comme un enjeu majeur de santé publique. Concernant l'optimisation du mode de reconditionnement, la mise au point d'un modèle préclinique porcin parfaitement reproductible a permis de mettre en évidence une supériorité de la CRN sur le RIS. Une durée de CRN de 4 heures minimum sans dépasser 6 heures paraît optimale. Concernant la conservation hypothermique, les MPH permettent le maintien du niveau d'expression des gènes retrouvé en fin de CRN. L'ajout d'une oxygénation active en MPH ou de curcumine en solution statique améliore le devenir du greffon à court et long termes dans un modèle préclinique d'autogreffe. Ce travail pourrait s'étendre à l'étude d'autres organes, d'autres durées d'ischémie chaude et aux DDAC contrôlés afin d'élargir encore le nombre d'organes éligibles à la transplantation. / Transplantation is the best alternative to end-stage renal disease. The shortage of grafts led the transplant teams to consider uncontrolled deceased donors after circulatory death (DCDs). These grafts suffered from a period of warm ischemia and are more vulnerable. Reconditioning methods in the donor by in situ cooling (ISC) and normothermic regional perfusion (NRP) have been developed to reduce the ischemia-reperfusion injuries. Each team has the choice as to the method and there are many different practices. After removal of kidneys, the use of hypothermic perfusion machines (HPM) is generally recommended. The optimization of reconditioning in the donor and hypothermic preservation appears as a major public health challenge. About optimization of the reconditioning method, the development of a high reproducible preclinical porcine model allowed to highlight the superiority of RNP over ISC. NRP duration of 4 hours minimum without exceeding 6 hours seems optimal. About hypothermic preservation, HPM allows to maintain the level of expression of the genes found at the end of RNP. The addition of active oxygenation to HPM or curcumin in static solution improves the graft outcomes in the short and long terms in a preclinical model of auto transplantation. This work could be extended to the study of other organs, other durations of warm ischemia and to controlled DCDs in order to further increase the number of transplantable grafts.